A combustion arrangement of a gas turbine usually comprises a combustion chamber which is arranged within an outer casing and which defines a space for burning a mixture of fuel and compressed air. One example of such a combustion arrangement is a dry low emission (DLE) combustion arrangement which operates on a lean mixture of fuel and compressed air, thereby producing a low amount of emissions, (e.g., different kinds of nitrogen oxides and carbon monoxide).
It may be commonly known that pressure oscillations may arise within the combustion chamber during operation of the gas turbine which may influence operational conditions of the combustion chamber and which may thus hamper a performance or life of the combustion chamber. In particular, the performance or efficiency of the gas turbine may be reduced due to these oscillations.
These pressure oscillations may be generated due to combustion flow dynamics of gases within the combustion chamber, particularly due to the lean mixture of air and fuel which is used for DLE. Combustion flow dynamics may be generated by flame excitation or aerodynamic induced excitation within the combustion chamber during the burning process. Further, insufficient damping of a housing of the combustion chamber may also contribute to pressure oscillations within the combustion chamber, since oscillations of the housing may change the space defined by the combustion chamber housing.
Further pressure oscillations within the combustion chamber may evolve due to gas flow dynamics particularly of compressed air (as an oxidant of the combustion process) in a space defined between the outer wall or casing of the combustion arrangement and an outer wall of the combustion chamber particularly upon this gas flow entering the combustion chamber. For example, when a swirler is arranged at a supply inlet or port of the combustion chamber, flow dynamics within the combustion chamber may be modified such that pressure oscillations within the combustion chamber may arise. It may be generally desired that a gas inlet flow comprising a high Mach number may be present to decouple the combustion chamber from pressure oscillations arising from an outer flow surrounding the combustion chamber.
In order to damp such pressure oscillation within the combustion chamber, different measures are known. A geometry of the combustion chamber may be modified in that, for example, a length extension of the combustion chamber may be changed.
Further, a damping device may be arranged within the combustion chamber or outside of the combustion chamber, in order to damp the amplitude of particular frequencies or even frequency spectra of the pressure oscillations. Such damping devices may be particularly arranged at pressure oscillation anti-nodes. Arranging damping devices in such a way that the damping devices may surround the combustion chamber but being spaced from an inlet supply to the combustion chamber may offer an undisturbed gas flow (in particular flow of compressed air) into the combustion chamber. However, the full load characteristics of the combustion chamber may be altered, eventually leading to increased combustion dynamics within the combustion chamber in terms of unintentionally generating oscillation resonance of pressure oscillations within the combustion chamber. A frequency or frequency spectrum of pressure oscillations within the casing of the combustion chamber and/or a vortex shedding may then not sufficiently be damped.
Most DLE combustion systems are prone to combustion dynamics due to a lean mixture of air and fuel (to produce low amounts of nitrogen oxides). Combustion dynamics may arise as a result of flame excitation, aerodynamics-induced excitation or insufficient clamping. U.S. Pat. No. 4,122,674 discloses a burner can, including a noise suppressing cavity, for use in the combustor assembly of a gas turbine engine to minimize the combustion noise emitted by the engine, wherein the cavity is mounted at an end of the burner can that includes a fuel nozzle for injection of fuel into the interior of the burner can and is in acoustic communication with the interior of the burner can via a perforated metal sheet that forms a partition between the burner can and the cavity.
However, the above described measures may result in a poor damping of pressure oscillations within the combustion chamber.